Daniel F. Kripke, M.D. has studied the relationship between biological rhythms and depression since the early 1970s. He states that seasonal responses in many mammals are controlled by the photoperiod. Therefore, it seemed that depression might be analogous to winter responses and that light might be an effective treatment.
The "time has come to accept bright light treatment into our therapeutic armamentarium," urged Daniel F. Kripke, M.D., professor of psychiatry at the University of California San Diego. Kripke has studied the relationship between biological rhythms and depression since the early 1970s. In an interview with Psychiatric Times, Kripke discussed two theories of phototherapy.
"We know that seasonal responses in many mammals are controlled by the photoperiod...We know that the lethargy, changes in appetite and loss of sexual interest seen in many small mammals in the winter are, in fact, controlled by the reduced daylight...Such mammals increase their activity, sexuality and aggressiveness in the summer, because the days are longer. From that knowledge, it seemed that depression might be analogous to winter responses and that light might be an effective treatment. That is one plausible theory.
"There also is a theory based on the finding that there are some timing abnormalities of circadian rhythms in many depressed patients, and that because light can correct timing abnormalities, it might work," he added. "As of today, there is evidence for both theories and evidence against both theories. I don't believe the theoretical basis is yet established. Nevertheless, the treatment [has been] tried and it works."
Numerous trials from Europe, Japan and the United States indicate that bright light is beneficial in treating nonseasonal as well as seasonal depression (Dietzel et al., 1986; Kjellman et al., 1993; Levitt et al., 1991; Peter, 1986; Yamada et al., 1995), Kripke pointed out.
"The response [to light therapy] is quite rapid, often within a week or two, which is more rapid than the response to antidepressant drugs or psychotherapy," he said.
(Other studies have found modest or no clear benefit to bright light therapy for nonseasonal depression [Mackert et al., 1990; Szadoczky et al., 1991; Thalen et al., 1995]-Ed.)
Kripke and his colleagues also have conducted clinical studies of bright light. As early as 1981, he reported that bright light had an antidepressant effect among patients with nonseasonal major depressive disorders. Although a single hour of light treatment produced only about a 12% reduction in depression ratings as compared to placebo, the result was statistically significant in the first seven patients.
In 1992, Kripke and colleagues reported on their one-week study of veterans with depression who were hospitalized in a Veterans Affairs Medical Center. The veterans had nonseasonal major depressive disorders or depressed forms of bipolar disorder. Additionally, the majority of the patients had comorbidities, such as substance use disorders. Twenty-five patients were randomly assigned to bright white light treatment (2,000 to 3,000 lux) and 26 patients were randomized to dim red light placebo-control treatment.
"Within one week of bright light treatment, the 25 patients reduced their depression scores about 18%, whereas the 26 placebo patients didn't improve at all," Kripke said.
Currently, a study is being conducted by Kripke's colleague, Richard Loving, Ph.D., R.N., in the department of psychiatry, University of California San Diego. Loving has been studying unipolar nonseasonally depressed outpatients who are being treated with antidepressants along with a half-night of sleep deprivation followed by administration of bright light therapy.
"There is evidence that a half-night of sleep deprivation may augment the bright light response," Kripke said. "Indeed, Loving has found that with this triple combination, the patients given the bright light had a 30% improvement within a week as compared to the group treated with placebo light and otherwise the same medication and sleep deprivation. That is a very dramatic response of a similar or greater magnitude than one might obtain with Prozac [fluoxetine] in 12 to 16 weeks. That study is very small and still going on, but it resembles the study done by Neumeister  at the University of Vienna on inpatients with about the same results."
For patients with major depressive disorder, Neumeister and colleagues studied whether light therapy beginning in the morning after a partial-sleep deprivation is able to prevent a relapse after sleep deprivation. (In some patients with major depressive disorder, partial-sleep deprivation results in a pronounced decrease of depressive symptoms. However, the beneficial effect is usually lost after one night of recovery sleep.) In the study, all patients received an antidepressant medication, which was kept constant before and during the study period. Neumeister and colleagues found that bright light prolonged the antidepressant effects of partial-sleep deprivation for up to seven days.
Based on these studies, Kripke believes "a clinician would be wise to go ahead with standard therapy and add bright light." He added, "I would only recommend using bright light alone for the patient who for some reason didn't want to accept or couldn't tolerate standard treatment. Pregnant women, young children whose parents are nervous about starting them on a drug regimen, or patients who had allergic reactions or other side effects with antidepressants would be common examples."
Another candidate group might be depressed individuals not currently receiving treatment, Kripke suggested.
"We know that the majority of Americans who are depressed are not asking for [or] receiving treatment. So there is a very large portion of the depressed population that, for philosophic reasons, doesn't want to avail themselves of standard treatment, but they might be more willing to use bright light."
For his own patients who are suffering from a newly diagnosed seasonal or nonseasonal depressive disorder, Kripke said he would provide standard treatment (antidepressant drug and some psychotherapy) as well as bright light therapy.
"If the situation was rather severe and the need for response urgent, I might suggest that the patient get up in the middle of the night on the day before the first light treatment," he said. While acknowledging that "the sleep deprivation part of it needs more study," Kripke said, "the addition of light to standard treatment is ready for clinicians to use.
"There is now plenty of evidence that adding light will help the patient at least in the first week or two of treatment when the antidepressant drugs don't actually do that much," he said.
Kripke is not aware of any controlled data in seasonal affective disorder or nonseasonal depressed populations showing that adding bright light therapy to standard treatment improves outcome, although he said each modality "works alone." Many clinicians, he added, using light therapy to treat patients with seasonal affective disorder do eventually include medications.
Bright light therapy must be consistent with the patient's habits, according to Kripke.
"The most important decisions are whether to give the patient bright light through going outdoors, through changes in room lighting or through buying a light box," he said.
Advising patients to spend more time outdoors can work well in Southern California but not in areas with harsher climates, Kripke said. In many circumstances, it also is possible to increase ordinary room lighting, and sometimes that will be of considerable benefit.
To clarify, Kripke pointed out that on a sunny day outdoors, illumination might be about 10,000 lux looking towards the horizon. However, people spend most of their time indoors in environments with lighting between 50 and 500 lux. In the evening, the average living room might be lit at about 15 lux, but some people watch television in rooms as dim as 1 lux, which is about the same as the light of the full moon.
"We have evidence that people who are outdoors at least one hour a day are less depressed and report fewer sleep complaints in the general population. Such a study doesn't prove causality, but since we have shown beneficial effects in experimental studies, it is reasonable to think that a large segment of the population, which isn't in daylight even an hour per day, is causing themselves problems."
In a book chapter, "The Uses of Bright Light in an Office Practice," Kripke pointed out that there is a trend for people who experienced less bright lighting to report more depression (Kripke, 1998b). Therefore, he prescribes a special light box that is available through a number of manufacturers for approximately $200 to $400 (Table). Generally, the light boxes contain fluorescent bulbs, which use less electricity and radiate less heat than incandescent lights.
"Because the fluorescent light boxes produce quite diffuse light, you can look at them directly, whereas with very bright incandescent light such as that produced by halogen bulbs, the light comes from a very small point, which is really too bright to look at directly with safety," he said.
In general, 200 to 300 watts of fluorescent light illuminating a bright diffuser about one yard from the eyes will give about 2,000 to 3,000 lux. Some bigger higher wattage light boxes placed 12 to 18 inches from the patient's eyes will give off 10,000 lux.
Kripke also addressed dosage strategies in the chapter. "Just like with any medical treatment, [depressed patients] vary in the dose they need," he said. The amounts of light needed are somewhere in the range required to bring a depressed person above the average for daily light exposure, Kripke wrote. That can be achieved with as little as 15 to 30 minutes of very bright light (approaching 10,000 lux) or with a few hours of light of 2,000 to 3,000 lux (like a cloudy day in the shade).
For mild depression accompanying advanced sleep-phase in the elderly, modest amounts of lighting may be sufficient, he wrote. But for cases of severe depression, light much dimmer than 2,000 lux is not likely to be effective without many hours of daily exposure.
For many patients, bright light at any time of day helps depression, according to Kripke, but there is some evidence that seasonal affective disorder (SAD) patients may do a bit better with morning light (Ruhrmann et al., 1998). This may be due in part to SAD patients' tendency to sleep late rather than the seasonality of their depression, Kripke wrote.
It is the sleep pattern that provides the most useful clue to optimal timing, he added. Patients whose depression is linked to hypersomnia tend to do best with light in the morning. For such patients, the hour immediately after awakening is the most effective time to use bright light. For the patient who nods off early in the evening and cannot stay awake for prime-time television, Kripke recommended evening bright light.
If the physician has a patient who may be bipolar, Kripke said it might be safer to use evening light, because the risk of mania appears to be less with evening rather than morning light. "I don't recommend using bright light for depressed bipolar patients unless they are receiving a mood stabilizer, because in 1% or 2% of cases, bright light will trigger serious mania in a bipolar patient," he noted. "The duration of bright light treatment in a depressed bipolar patient must be individualized."
In studies of light box therapy, Kripke said some minor side effects (e.g., nausea, headache and eye irritation) have been reported, but they "generally involve no permanent risk and usually not enough discomfort to require discontinuation."
(When adjunct light therapy was used with trimipramine [Surmontil], Muller et al.  did report some side effects, such as aggravated sedation and decreased appetite-Ed.)
With regards to duration of bright light therapy, Kripke wrote that many people who benefit from it need to use it for years.
"If they discontinue using light, after a few weeks, they may relapse into depression again. Some people find they need less time with their light box to avoid relapse than they did to make the depression go away at the beginning," he wrote. "Therefore, after at least two to three months of remission, it could be reasonable to try slowly reducing the light dose, to see if symptoms recur."
To help guide clinicians in the use of light therapy, Kripke recommended the following resources: the book Sleep Disorders edited by Poceta and Mitler, in which Kripke has a chapter; his 1998 article in the Journal of Affective Disorders; a chapter on light therapy by Norman Rosenthal, M.D., who is with the Clinical Psychobiology Branch at the National Institute of Mental Health, in In Treatment of Psychiatric Disorders (Rosenthal, 1995); and several articles published in the Journal of Biological Rhythms (Campbell et al., 1995; Dijk et al., 1995; Terman et al., 1995); and the Society for Light Treatment and Biological Rhythms, New Haven, Conn.,.<HTTP://WWW.WEBSCIENCES.ORG/SLTBR/>
Based on his extensive work with bright light therapy, Kripke believes it is an effective and cost-efficient addition to modern health care:
"It is a wonderful thing to be able to offer patients this simple and safe treatment and see them become happier faster."
Campbell SS, Dijk DJ, Boulos Z et al. (1995), Light treatment for sleep disorders: consensus report. III. Alerting and activating effects. J Biol Rhythms 10(2):129-132.
Depression Guideline Panel (1993), Depression in Primary Care: Volume 2. Treatment of Major Depression. Washington, D.C.: Agency for Health Care Policy and Research, AHCPR Publication No. 93-0551, U.S. Government Printing Office.
Dietzel M, Saletu B, Lesch OM et al. (1986), Light treatment in depressive illness. Polysomnographic, psychometric and neuroendocrinological findings. Eur Neurol 25(suppl 2):93-103.
Dijk DJ, Boulos Z, Eastman CI et al. (1995), Light treatment for sleep disorders: consensus report. II. Basic properties of circadian physiology and sleep regulation. J Biol Rhythms 10(2):113-125.
Kjellman BF, Thalen BE, Wetterberg L (1993), Light treatment of depressive states: Swedish experiences in latitude 59 north. In: Light and Biological Rhythms in Man (Wenner-Gren International), Wetterberg L, ed. Stockholm: Pergamon Press, pp 351-370.
Kripke DF (1998a), Light treatment for nonseasonal depression: speed, efficacy and combined treatment. J Affect Disord 49(2):109-117.
Kripke DF (1998b), The uses of bright light in an office practice. How to brighten up your patients. In: Sleep Disorders: Diagnoses and Treatment, Poceta JS, Mitler MM, eds. Totowa, N.J.: Humana Press.
Kripke DF (1981), Photoperiodic mechanisms for depression and its treatment. In Biological Psychiatry 1981: Proceedings of the IIIrd World Congress of Biological Psychiatry Held From June 28th to July 3rd, 1981 in Stockholm, Sweden. Perris C, Struwe G, Jansson B, eds. New York: Elsevier-North Holland Biomedical Press, pp 1249-1252.
Kripke DF, Mullaney DJ, Klauber MR et al. (1992), Controlled trial of bright light for nonseasonal major depressive disorders. Biol Psychiatry 31(2):119-134.
Levitt AJ, Joffe RT, Kennedy SH (1991), Bright light augmentation in antidepressant nonresponders. J Clin Psychiatry 52(8):336-337.
Mackert A, Volz HP, Stieglitz RD et al. (1990), Effect of bright white light on nonseasonal depressive disorder. Pharmacopsychiatry 23(3):151-154.
Muller MJ, Seifritz E, Hatzinger M et al. (1997), Side effects of adjunct light therapy in patients with major depression. Eur Arch Psychiatry Clin Neurosci 247(5):252-258.
Neumeister A, Goessler R, Lucht M et al. (1996), Bright light therapy stabilizes the antidepressant effect of partial sleep deprivation. Biol Psychiatry 39(1):16-21.
Peter K, Rabiger U, Kowalik A (1986), [Initial results with bright light (phototherapy) in affective psychosis]. Psychiatr Neurol Med Psychol (Leipz) 38(7):384-390.
Rosenthal NE (1995), Light Therapy. In Treatment of Psychiatric Disorders, Gabbard GO, ed. Washington, D.C.: American Psychiatric Press Inc., pp 1263-1273.
Ruhrmann S, Kasper S, Haweliek B et al. (1998), Effects of fluoxetine versus bright light in the treatment of seasonal affective disorder. Psychol Med 28(4):923-933.
Szadoczky E, Falus A, Nemeth A et al. (1991), Effect of phototherapy on 3H-imipramine binding sites in patients with SAD, non-SAD and in healthy controls. J Affect Disord 22(4):179-184.
Terman M, Lewy AJ, Dijk DJ et al. (1995), Light treatment for sleep disorders: consensus report. IV. Sleep phase and duration disturbances. J Biol Rhythms 10(2):135-147.
Thalen BE, Kjellman BF, Morkrid L et al. (1995), Light treatment in seasonal and nonseasonal depression. Acta Psychiatr Scand 91(5):352-360.
Yamada N, Martin-Iverson MT, Daimon K et al. (1995), Clinical and chronological effects of light on nonseasonal affective disorders. Biol Psychiatry 37(12):866-873.